This invention relates generally to a walking beam type oil well pumping unit, and in particular to an improved means for connecting the walking beam and equalizer beam of such a unit.
In a typical walking beam type oil well pumping unit, a walking beam is pivoted at the upper end of a samson post and has a horse head at its front end which supports a polished rod that reciprocates in the well opening. The walking beam is rocked on the samson post by a motor which rotates two counterweighted cranks in vertical planes parallel to that of the walking beam. The lower end of a pitman arm is pivotally connected to each crank. The upper ends of the two pitman arms are connected to opposite ends of an equalizer beam, the latter being connected to the rear end of the walking beam so that the motion of the cranks is transferred through the pitman arms and equalizer beam to the walking beam.
The walking beam is typically connected to the equalizer beam by means of a tail shaft rotatably mounted on the walking beam perpendicular to the axis of the walking beam and parallel to the axis of the equalizer beam. The tail shaft is journaled in a bearing supported by a bracket depending from the rear end of the walking beam. In one design, the ends of the tail shaft are held in split mounts secured to the equalizer beam. Each mount comprises a base with a semicylindrical groove and a cap with a complementary semicylindrical groove which together form a cylindrical opening for receiving a respective end of the tail shaft. The cap and base are bolted to the equalizer beam. Due to the design of the pump unit, the bolts are under a cyclical tensile load; and if they are not properly torqued when they are installed, the cyclic loading may cause premature fatigue failure. The installation in the field thus requires skill and care and is time consuming. Even when the bolt is properly installed, it is still prone to fatigue failure.
In another prior system, the tail shaft is rotatable in a bearing housing with its ends held in a pair of pinch blocks welded to the equalizer beam, the size of the shaft openings in the pinch blocks being adjustable by bolts. The bearing housing includes a sleeve perpendicular to the tail shaft, by which the housing can be mounted to the walking beam with a pin. This system requires very precise manufacture to insure proper alignment of the components when assembled. The pinch block bolts are also subject to cyclic loading.